hi, thanks for this

can I Route on cookies, similar to this question: Is it possible to modify Router matches based on cookies like in Varnish? - #3 by dimitarvp

I want to be able to present a static cached page using http_cache | Hex if no cookies and if there are cookies I want to route to a non cached cookied page

in Varnish you can do:

sub vcl_hash {
  if (req.http.cookie ~ "wordpress_logged_in_") {
    hash_data("wordpress_logged_in");
  }
  # the builtin.vcl will take care of also varying cache on Host/IP and URL 
}

or better

import cookie;
import directors;
import std;
import kvstore;

sub vcl_init {
    kvstore.init(0, 1000);
}

sub vcl_backend_response {
    set beresp.http.x-tmp = regsub(header.get(beresp.http.set-cookie,"JSESSIONID=", " *;.*", "");
    if (beresp.http.x-tmp != "") {
        kvstore.set(0, cookie.get("id"), beresp.backend, 15m);
    }
    unset beresp.http.x-tmp;
}

sub vcl_recv {
    cookie.parse(req.http.cookie);
    set req.http.server = kvstore.get(0, cookie.get("id"), "none");

    if (req.http.server == "s1") {
        set req.backend_hint = s1;
    } else if (req.http.server == "s2") {
        set req.backend_hint = s2;
    } else {
        if (std.rand(0, 100) < 50) {
            req.backend_hint = s1;
        } else {
            req.backend_hint = s2;
        }
    }
    return (pass);
}

https://varnish-cache.org/docs/trunk/reference/vmod_cookie.html

or in Nginx, you can define a map in http section:

map $cookie_proxy_override $my_upstream {
  default default-server-or-upstream;
  ~^(?P<name>[\w-]+) $name;
}

Then you simply use $my_upstream in location section(s):

location /original-request {
  proxy_pass http://$my_upstream$uri;
}

Nginx evaluates map variables lazily, only once (per request) and when you are using them.

server {
    ...
    set $upstream "default-server-or-upstream";
    if ($http_cookie ~ "proxy_override=([\w-]+)") {
        set $upstream $1;                                   
    }

    location /original-request {
        proxy_pass http://$upstream/original-application
    }
}

I asked Brave search AI and it gave me:

defmodule MyApp.Router do
  use Plug.Router

  plug :match
  plug :dispatch

  get "/hello" do
    case get_req_header(conn, "cookie") do
      [{"cookie_value"}] -> send_resp(conn, 200, "Cookie matched")
      _ -> send_resp(conn, 400, "Cookie not matched")
    end
  end
end

or

defmodule MyApp.Router do
  use Plug.Router

  plug :match
  plug :dispatch

  get "/set-cookie" do
    domain = PublicSuffix.registrable_domain(conn.host)
    opts = [store: :cookie, key: "_myapp_key", signing_salt: "asdadl", domain: domain, max_age: max_age, http_only: true]
    opts = Plug.Session.init(opts)
    conn = Plug.Session.call(conn, opts)
    send_resp(conn, 200, "Cookie set")
  end
end

@tangui